England midfielder Dele Alli will undergo a scan on Tuesday on the thigh injury he sustained against Tunisia.
Alli seemed to be struggling towards the end of the first half in Volgograd but stayed on until the 80th minute, when he was replaced by Ruben Loftus-Cheek.
Harry Kane's late winner secured England a 2-1 opening victory in Group G and Alli looked dangerous, particularly during an excellent early spell for Gareth Southgate's side.
The 22-year-old has six days to recover before Sunday's game against Panama, with Marcus Rashford and Loftus-Cheek both potential replacements.
"We had to keep monitoring Dele," Southgate said after the match on Monday.
"He was feeling a little bit of an issue just before half-time but felt he could carry on and I thought the runs that he was making and the way he was pressing the ball was still causing a problem."